1. Field of the Invention
The invention relates to a disposable injection syringe and in particular to an injection syringe having a cylindrical liquid container with needle connection means at one container end and a plunger in the container for movement by a plunger rod so as to eject material to be injected.
In the design of such syringes reduction of the amount of liquid remaining is desirable. The development of new medicines involves steadily increasing costs for research in an industry which is heavily research-based, particularly because of the requirements imposed on new medicines by national authorities and advances in medical science, so that the costs of medicines are rising continually. Further, in a continuing effort to minimize the quantity of material being administered to patients, there is a trend to administer relatively smaller quantities of injection liquid than previously, and therefore injection syringes with smaller capacities are desirable. Another disadvantage of a large quantity of unusable injection liquid is that is may needlessly impair the environment when a used syringe is destroyed.
2. Description of the Prior Art
Injection syringes, both disposable and reusable, have been used for many years for injection of medicines into patients. All of these syringes have had the disadvantage that not all the liquid contained within the syringe can be administered. In part, this occurs because a quantity of injection liquid remains in the needle; however, at least part of the disadvantage arises because the plunger cannot be moved entirely to the end of the liquid-containing portion of the syringe, that is, to the beginning of the needle. Thus there is often a quantity of injection liquid left between the plunger piston and the beginning of the needle.
This problem is particularly noticeable in disposable syringes which are pre-filled with medicine by the manufacturer. To permit long storage times of such pre-filled syringes without excessive degradation of the medicine, in most cases it is necessary to protect the injection liquid from deterioration which would result from extended contact with the material from which the needle or needle connection means are made, these devices usually being made from a metal or a synthetic resin. Therefore a sealing member is often provided at the needle end of the liquid container, the sealing member being manufactured from a rubber material of a pharmaceutical quality, or from a corresponding chemically inert material. The plunger is made from materials which are similarly selected. As a result, during storage the injection liquid contacts only the materials from which the liquid container, the plunger and the sealing member are made.
Disposable syringes of the previously known types have an obstruction or an inwardly extending flange which is formed by a portion of the liquid container itself at the needle connection end. This flange can serve both for attachment of the needle hub, and as a stop, limiting the motion of the plunger, and thereby resulting in the formation of a central region within the constriction, wherein unused injectable liquid collects. Normal injection syringes of the types described above, depending on their capacity, generally contain a volume between 0.1 and 0.3 ml of unusable injection liquid. Reduction of this unusable quantity to a minimum is desirable, particularly where expensive medicines are involved or injection syringes of small capacity are to be used.